Revert "Add a hook to validate account creation fields."

Change adds a hook that serves exactly the same purpose as
AbortNewAccount. Also change was merged prematurely and is
missing message documentation as well as having some minor
code flow issues.

This reverts commit cc1006b77c6dfdc53266e0bfc73fc9daf304f8e7.

Change-Id: I8656aa1a99c84778fd85ec7da9d6ce23bd6cf9b9
Merge "Revert "Add a hook to validate account creation fields.""